Recently, communication services with large communication capacity, including video service for smartphones, have been provided. Accordingly, there is a need for greatly increasing the existing communication capacity and a DWDM (Dense Wavelength Division Multiplexing) type communication has been adopted to increase communication capacity using optical fibers that were installed already. The DWDM type communication simultaneously transmits light having several wavelengths through one optical fiber, using a phenomenon that light signals having several wavelengths do not interfere with each other even if they are simultaneously transmitted through one optical fiber, because lasers having different wavelengths do not interfere with each other.
At present, NG-PON2 (Next Generation—Passive Optical Network version 2) is internationally under consideration as a standard and a tunable laser capable of having four channels with a frequency separation of 100 GHz was selected, as an optical communication standard to be installed for subscribers, for NG-PON2. As an optical module for subscribers for NG-PON2, an SEP (Small Form factor Pluggable) transceiver module is the standard and the SFP module package is small in volume, so it is required to reduce the size of the 4-channel tunable laser module.
At present, various types of tunable lasers are on the market, but most of them have an optical device with a large volume in the type of a butterfly packet, so the optical device having a large volume cannot he mounted in the SFP transceiver module. A TO (transistor outline) type package is an optical package that can be mounted in the SFP transceiver, but a tunable TO type optical device that can be tuned in a TO type has not been proposed yet.